EXTENSIONS OF DARWINISM 281 



and archaic reptiles. There were, however, a considerable 

 number of primitive centipedes, spiders, Crustacea, and even 

 true insects, the latter having already become specialised into 

 several of our existing orders. All these occur either in the 

 Coal formation of Europe or the Devonian rocks of North 

 America, which seems to imply that when land-vegetation 

 first began to cover the earth a very long period elapsed 

 before any correspondingly abundant animal life was 

 developed ; and this was what we should expect, because it 

 would be necessary for the former to become thoroughly 

 established and developed into a sufficient variety of forms 

 well adapted to all the different conditions of soil and 

 climate, in order that they might be able to resist the 

 attacks of the larger plant-feeding animals, as well as the 

 myriads of insects when these appeared. So far as we can 

 judge, the vegetable kingdom was left to develop freely 

 during the enormous series of ages comprised in the 

 Devonian, Carboniferous, and Permian formations, to which 

 we must add the gap between the latter and the Triassic — 

 the first of the Secondary formations. By that time the 

 whole earth had probably become more or less forest-clad, 

 but with vegetation of a low type mostly allied to our ferns 

 and horse-tails, with some of the earliest ancestral forms of 

 pines and cycads. 



In the succeeding Secondary era the same general type 

 of vegetation prevailed till near its close ; but it was then 

 everywhere subject to the attacks of large plant-devouring 

 reptiles, and under this new environment it must necessarily 

 have started on new lines of evolution tending towards those 

 higher flowering plants which, throughout the Tertiary 

 period, became the dominant type of vegetation. It seems 

 probable that throughout the ages animal and vegetable 

 life acted and reacted on each other. The earliest luxuriant 

 land-vegetation, that which formed the great coal-fields of 

 the earth, was probably adapted to the physical environ- 

 ment alone, almost uninfluenced by the scanty animal life. 

 Then reptiles and mammals were differentiated ; but the 

 former increased more rapidly, being perhaps better fitted to 

 live upon the early vegetation and to survive in the heavy 

 carbonated atmosphere. This in turn became more varied and 



